Conventionally, soaps; anionic surfactants such as sodium dodecylbenzenesulfonate, polyoxyethylene alkylphenyl ether sulfuric acid ester salts, polyoxyethylene aralkyl aryl ether sulfuric acid ester salts, polyoxyethylene alkyl ether sulfuric acid ester salts, etc.; and nonionic surfactants such as polyoxyethylene nonylphenyl ether, polyoxyethylene aralkyl aryl ethers, polyoxyethylene alkyl ethers, etc. have been utilized as an emulsifier for emulsion polymerization. However, in polymer films obtained from a polymer dispersion using such an emulsifier, the used emulsifier remains in a liberated state in the polymer film, and hence, there is involved such a problem that water resistance and adhesion of the film are inferior, or the like. Then, as remedial measures of the above-described problem, reactive emulsifiers having a copolymerizable unsaturated group have been proposed (for example, PTL 1 to PTL 3).
Though reactive emulsifiers having an acryl group or a methacryl group as a copolymerizable unsaturated group, which have been conventionally proposed, are excellent in copolymerizability with monomers, they encounter such a problem that polymerization stability at the time of emulsion polymerization is deteriorated. For example, there are involved such problems that a lot of agglomerates are produced during the emulsion polymerization; the formed particles are coarse; and stability with time is inferior, and the like. In addition, as for reactive emulsifiers having an allyl group as a copolymerizable unsaturated group, there may be the case where copolymerizability of the reactive emulsifier with monomers is inferior depending upon the monomer species or polymerization condition. Also, a problem that polymer films obtained from a polymer dispersion, which are thoroughly satisfactory in water resistance and adhesion, are not obtained; and a problem that a process trouble is caused due to foaming of a polymer dispersion remain. In particular, the above-described problems are often generated in the case where styrene is contained as a polymerizable unsaturated monomer at the time of emulsion polymerization, and it is eagerly demanded to solve these problems in the commercial production.